Many people are concerned about our dependence upon foreign energy sources. In addition there are environmental issues in using coal and other carbon based fuels. As a result there is a greater desire to use solar energy for more of our energy needs.
One problem with solar energy has been the relatively high cost of solar cells that are used to generate electricity. The materials used in the solar cells, i.e. the silicon wafers and silver ribbons, are fairly expensive. Their cost of manufacture is also high.
Solar collectors have also been used for a number of years for heating water. A solar collector is often secured to a roof or wall surface and positioned so it is facing the sun. The sun heats water or a working fluid that passes through piping in the collector. A pump or natural convection transports the heated fluid to a heat exchanger or a storage tank for use by occupants of the building. Sometimes a parabolic mirror is used to concentrate the sunlight on the tube containing the fluid.
One issue that has inhibited the use of solar collectors has been the relatively low temperatures that are achieved using these devices. Except for really sunny days a supplemental system may also be necessary to really heat the water to high enough temperatures for most uses.